In a manner known in itself, a turbomachine compressor comprises:                several compression stages, each composed of a bladed rotor and a bladed stator,        a flowpath in which the rotor blades and the stator vanes are located.        
The flowpath may be delimited between an outer casing and an inner casing, or between an outer casing and a central hub.
There is a functional clearance in the flowpath between the blades of each rotor and the wall of the outer casing. Similarly, there is a functional clearance between the blades of each stator and the wall of the inner casing or the hub. Secondary flows pass through these functional clearances in the opposite direction (from the downstream side towards the upstream side) to the direction of the main flow (from the upstream side towards the downstream side) that are parasite flows. Those skilled in the art would generally like to eliminate or reduce parasite airflows that develop inside the compressor and that reduce the aerodynamic efficiency of the compression stage. In practice, the compressor structure is designed so as to minimize these clearances and therefore parasite flows.
With the same objective of improving operation of a compressor, it is known that applying suction to the boundary layer of the main flow at one or several appropriate locations on the profile of the blades and vanes can improve the aerodynamic situation of a compression stage to increase the compression ratio of the stage without deteriorating its efficiency or its stall limit. This means that a compressor with a significantly smaller number of stages can be used than is possible with a compressor in which no suction is applied to the profiles, for a given compression ratio.
Document GB 1 085 227-A discloses vanes or blades in which cavities are formed connected to the surface of the blade by orifices. These orifices are located close to the trailing edge of the blades and can apply suction to suck in the boundary layer of the blades in their cavity. A passage passing through the base of each blade provides a communication between the cavity in this blade and a circuit inside the compressor, in which a suction pump is fitted. Controlling boundary layer flows in this way reduces turbulence inside the turbomachine, thus reducing the noise made by the turbomachine.
Document FR 2 166 494-A5 discloses suction openings formed in the wall of the compressor outer casing to eliminate the boundary layer that develops between the blades of the two successive compression stages. These suction openings are connected to suction means, for example such as a throttle and/or a flow regulator. Air sucked in is then rejected into the atmosphere or is reused.
Document FR 2 248 732-A5 discloses an improvement to FR 2 166 494-A5, the purpose of which is to eliminate or reduce the boundary flow layer along the outer casing of the compressor and the boundary flow layer along the blades. A boundary layer trap is formed in each blade, composed of a channel connected to boundary layer suction means. The channel opens up onto the suction face of the blade, in an area in which the curvature is changing. The suction means, similar to those in FR 2 166 494, are located in the casing or in the hub of the compressor. There are also openings provided in the wall of the compressor casing as in FR 2 166 494-A5.
Document WO 98/30802-A1 discloses vanes or blades in which cavities are formed. Nozzles, slits, porous or similar surfaces are provided through the vanes or blades to suck in the boundary layer of each blade into its inner cavity. The sucked in air is then transported in the cavity towards one end of the blade to be evacuated. When air is evacuated towards the end of a blade, it is evacuated outside the compressor through an opening in the outer casing of the compressor facing this blade and that opens up into a manifold, that prevents evacuated air from re-entering the compressor.
Document U.S. Pat. No. 6,004,095-A disclosed several arrangements of turbomachine compressors for blowing and/or sucking in air, and for circulating blown or sucked in air in order to reduce noise generated by the turbomachine.
In one arrangement disclosed in U.S. Pat. No. 6,004,095-A, the blades are provided with cavities. The cavities are connected to the surface of the blade through orifices through which air is sucked in. They are connected to an inner chamber in the compressor through a passage passing through their base, through which air is sucked into another part of the turbomachine. Suction is done using a pump.
In another arrangement disclosed in U.S. Pat. No. 6,004,095-A, the blades are provided with cavities. The cavities are connected to the surface of the blade through orifices through which air is sucked in. They are open near their end to a manifold with a porous wall through which air is sucked in towards a chamber located beyond the wall of the outer casing, through an opening formed in said wall. Slits can also be provided in the wall of the outer casing, on the upstream side of the blades to suck in the boundary layer of the wall of the outer casing towards said chamber. Suction is done by a pump.
In another arrangement disclosed in U.S. Pat. No. 6,004,095-A, the compressor is provided with guide vanes on the upstream side of the fan. Air originating from the low pressure compressor on the downstream side of the fan is returned through an inner chamber to the guide vanes, through their inner base and their outer base. As a variant, these guide vanes may also be fitted with one or several cavities connected at their surface through orifices and provided with passages passing through their base(s). Thus, air sucked in through the orifices is transported inside the cavity(ies) towards the hub and/or towards the rotor casing using a pump.
Therefore, the documents mentioned above describe arrangements including means of reducing or eliminating boundary layer flows that develop around the vanes or blades and/or along the outer casing of the compressor.
These arrangements use pumps or similar means as air suction means.